Saints turned down a £5million bid from Derby for striker Jones, complaining the bid "substantially undervalues" the player.
The Premier League new-boys returned with a second offer for Jones, 22, after having an initial bid for the Trinidad and Tobago international rejected last week.
A statement on the Saints official website read: "A further unsolicited and unwelcome approach from Derby County for Kenwyne Jones has been rejected.
"George Burley sees Kenwyne playing a major role in Saints' push for promotion this season.
"Moreover, it is considered that Derby County's latest offer to pay a total of £5million for the player very substantially undervalues his ability and potential as a Premiership-quality striker in the making.
"The club hope the rejection of Derby's latest offer will now bring the matter to a close."